Concrete is used more than any other manmade material on the planet. As of 2005, about six billion cubic meters of concrete are made each year, which equals one cubic meter for every person on Earth. More than 55,000 miles of freeways and highways in America are made of this material. The type of structure being built as well as the method of construction determines how concrete is placed and the composition of the concrete mix. Portland cement is the most common type of cement used in making concrete. It is a basic ingredient of concrete, mortar and plaster. Water is also commonly used for manufacturing concrete. The water to cement ratio (mass ratio of water to cement) is the key factor that determines the strength of concrete. In order to ensure economical and practical solutions to concrete needs, both fine and coarse aggregates are often utilized to make up the bulk of the concrete mixture. In addition, chemical admixtures in the form of powder or fluids are added to the concrete to give it certain characteristics not obtainable with plain concrete mixes. The most common types of admixtures are accelerators, retarders, air-entrainers that add and distribute tiny air bubbles in the concrete, plasticizers that increase the workability of fresh concrete, pigments, corrosion inhibitors, bonding agents and pumping aids.
There are several different types of concrete that are useful in different circumstances. For example, pervious concrete is sometimes specified by engineers and architects when porosity is required to allow some air movement or to facilitate the drainage and flow of water through structures. Additionally, pervious concrete pavement is an effective means to address important environmental issues and support sustainable growth. By capturing rainwater and allowing it to seep into the ground, porous concrete is instrumental in recharging groundwater, reducing stormwater runoff, and meeting US Environmental Protection Agency (EPA) stormwater regulations. The use of pervious concrete is among the Best Management Practices (BMPs) recommended by the EPA, and by other agencies and geotechnical engineers across the country for the management of stormwater runoff on a regional and local basis. Such pavement technology creates more efficient land use by eliminating the need for retention ponds, swales, and other stormwater management devices.